Observations of three high-state eclipse egresses of Hercules X-1.

Abstract

EXOSAT data from three high-state egresses of the pulsating X-ray binary Her X-1 are presented. Analysis of these data indicates that the extended atmosphere of the companion is the most likely explanation of the extent of the egresses. By fitting spectra taken from the egresses the authors find that the atmosphere has an exponential structure. If hydrostatic equilibrium is assumed, the derived temperature renders the atmosphere more luminous than is observed. A dynamical model is proposed in which the atmospheric scale height is enhanced by the action of the Coriolis force on flows driven along the stellar surface by the radiation pressure of the X-ray source. The particle density and temperature at the L1 point are not high enough to provide the observed accretion rate, if hydrostatic equilibrium is assumed.